Influence Of Electron Beam Parameters Research Articles

All-optical Compton scattering at shallow interaction angles

All-optical Compton sources combine laser-wakefield accelerators and intense scattering pulses to generate ultrashort bursts of backscattered radiation. The scattering pulse plays the role of a small-period undulator ( ${\sim }1\,\mathrm {\mu }{\rm m}$ ) in which relativistic electrons oscillate and emit X-ray radiation. To date, most of the working laser-plasma accelerators operate preferably at energies of a few hundreds of megaelectronvolts and the Compton sources developed so far produce radiation in the range from hundreds of kiloelectronvolts to a few megaelectronvolts. However, for such applications as medical imaging and tomography the relevant energy range is 10–100 keV. In this article, we discuss different scattering geometries for the generation of X-rays in this range. Through numerical simulations, we study the influence of electron beam parameters on the backscattered photons. We find that the spectral bandwidth remains constant for beams of the same emittance regardless of the scattering geometry. A shallow interaction angle of $30^{\circ }$ or less seems particularly promising for imaging applications given parameters of existing laser-plasma accelerators. Finally, we discuss the influence of the radiation properties for potential applications in medical imaging and non-destructive testing.

Passage of a focused electron beam generated by a forevacuum plasma source through a narrow extended metal cavity

We report on our investigations of the distribution of diameter of a focused electron beam along the propagation direction at the forevacuum pressures as a function of beam parameters and working gas pressure. The influence of electron beam parameters on the fraction of current transported through a narrow, extended tube is considered. We find that the angles of convergence and divergence of the focused beam depend on the position of the beam crossover point, and that maximum beam transmission through the tube is ensured at lower gas pressure and higher beam accelerating voltage. Up to 90% beam transmission efficiency is obtained for beam transport through a metal tube with diameter 8 mm and length 30 cm.

Surface treatment by the ion flow from electron beam generated plasma in the forevacuum pressure range

The paper presents research results of peculiarities of gas ion flows usage and their generation from large plasma formation (>50 sq.cm) obtained by electron beam ionization of gas in the forevacuum pressure range. An upgraded source was used for electron beam generation, which allowed obtaining ribbon electron beam with no transmitting magnetic field. Absence of magnetic field in the area of ion flow formation enables to obtain directed ion flows without distorting their trajectories. In this case, independent control of current and ion energy is possible. The influence of electron beam parameters on the parameters of beam plasma and ion flow – current energy and density – was determined. The results of alumina ceramics treatment with a beam plasma ions flow are given.

Surface treatment by the ion flow from electron beam generated plasma in the forevacuum pressure range

The paper presents research results of peculiarities of gas ion flows usage and their generation from large plasma formation (>50 sq.cm) obtained by electron beam ionization of gas in the forevacuum pressure range. An upgraded source was used for electron beam generation, which allowed obtaining ribbon electron beam with no transmitting magnetic field. Absence of magnetic field in the area of ion flow formation enables to obtain directed ion flows without distorting their trajectories. In this case, independent control of current and ion energy is possible. The influence of electron beam parameters on the parameters of beam plasma and ion flow – current energy and density – was determined. The results of alumina ceramics treatment with a beam plasma ions flow are given.

Nitriding of Stainless Steel in Electron-Beam Plasma in the Pulsed and DC Generation Modes

The influence of electron-beam parameters on the thickness and phase composition of a hardened layer formed upon the nitriding of austenitic stainless steel 12Cr18Ni10Ti in plasma produced by a beam in a low-pressure (3 Pa) nitrogen-argon mixture is studied. The results obtained in the DC and pulse-periodic modes of beam generation with the same mean current and electron energy are compared. In this case the negative bias voltage applied to the samples is 100 V. The nitriding temperature of 400°C is maintained at a mean beam current of 2.6 A and various combinations of frequency (100–500 Hz) and current pulse durations (0.1–0.3 ms) with an amplitude of 80 A. The mean ion-plasma current densities in the DC and pulsed modes are close in magnitude (2–3 mA/cm2 at 400°C). The high pulsed ion-current density (35–70 mA/cm2) creates conditions under which the surface sputtering rate during the pulse exceeds the growth rate of the nitrided layer. The nitriding of steel in the pulsed and DC modes over four hours gives the same result. Hardened layers with a thickness of 7–8 μm and a microhardness of the surface component of 15 ± 1 GPa in which the main phase is a supersaturated nitrogen solid solution (expanded austenite) are formed. A possible explanation is that nitriding in an electron-beam plasma proceeds mainly under the action of long-lived active neutral nitrogen particles rather than as a result of ion bombardment.

Dispersion characteristics of dielectric loaded metal grating

A novel type of slow-wave structure for Smith-Purcell device called dielectric loaded metal grating, is proposed in this article. The “hot” dispersion align of the structure is obtained by using the eigen-function method and single-mode approximation. The first-and second-order growth rate of beam-wave interaction are obtained at the synchronization point. The effects of grating groove width and depth on dispersion characteristic are analyzed, and the influences of electron beam parameters and distance between electron beam and grating surface on growth rate characteristic are also studied. The results show that dielectric-loaded metal grating can effectively weaken the structure dispersion, and that with the increases of relative dielectric permittivity, groove width and depth, the dispersion curve becomes flatter and moves toward low frequency. When the electron beam voltage or current changes, the first-order growth rate curve can only roughly describe the change trend, while the second-order growth rate can accurately show the change values. The simulation of the structure is performed by using two-dimensional particle-in-cell code MAGIC, and the simulation results accord well with the theoretical results.

Research on the Influence of Electron Beam Parameters on Molten Pool Morphologies during Electron Beam Melting Silicon

Electron beam melting is an effective method to remove volatile impurities in silicon, during which impurities such as P, Al and Ca etc. can be removed to less than 0.3×10-4wt.%. However, so far there is few research on the influence of electron beam parameters, such as beam density and beam size, on molten pool morphology, hence electron beam melting process has not been completely understood, which leads to low energy utilization. In this paper, on the basis of beam size calibration, the influence of beam density and beam size on molten pool morphology is investigated and the concept of melting angle is proposed to characterize molten pool morphology. At the same time, the optimal molten pool morphology for impurities removal and the corresponding electron beam parameters are also analyzed.

IFHTSE Global 21: heat treatment and surface engineering in the twenty-first century Part 15 – Progress in surface heat treatment using electron beam surface hardening

By using high frequency beam deflection techniques it is possible to carry out highly productive electron beam (EB) surface treatment. As a result of comprehensive investigations about the influence of EB parameters on structure and properties of the material in connection with EB hardening of steels and cast irons over the last 25 years, very interesting industrial applications are available now. The paper deals with the state of the art in this field.

Structure and Properties as a Result of Electron Beam Surface Treatment

A new generation of high frequency 3D deflection technique opens up manifold possibilities for a wider application of electron beam (EB) technologies for surface treatment. A high flexibility of process parameters connected with high productivity is obtained from the simultaneous interaction of the EB in several processing areas or by carrying out several processes simultaneously. The change of material and component‐specific surface properties can be adapted as required. An outstanding improvement of properties can be reached. Typical technological characteristics are explained and the influence of EB parameters on microstructure and properties is discussed. It has been shown that the EB is becoming more and more attractive and important for industrial applications of thermal surface technologies such as hardening, combined thermochemical treatment/hardening, remelting, surface alloying and dispersing

Influence of electron-beam parameters on the radiation-induced formation of graphitic onions

It is shown that to form spherical graphitic onions by intense electron bombardment of graphitized carbon inside the electron microscope, irradiation must be performed at energies above the threshold of elastic atomic displacement, and at beam current densities higher than about 150 A cm −2. Under these strong non-equilibrium conditions, it is possible to obtain the dynamic stability of the spherical shells, which appear fundamentally unstable in absence of irradiation.